A transmitting and receiving system represented by a digital television broadcasting has recently come into use. In this system, a media data signal such as a video-audio signal is digitized, and the media data signal is transmitted and received through various networks such as networks using a communication satellite and a broadcasting satellite. This system has a large number of transmission channels (or services) such as tens of channels or hundreds of channels. Therefore, it is expected that it is difficult to select a desired broadcast program from a large number of broadcast programs on a receiving side. To avoid this difficulty, a program selecting method has been proposed for the purpose of supporting the program selection. In this program selecting method, data of an electronic program guide is multiplexed with a media data signal such as a video-audio signal and is transmitted simultaneous with the media data signal, and each viewer of a program receiving side selects a desired broadcast program with reference to the electronic program guide data.
This electronic program guide data is useful to select a broadcast program on the program receiving side. However, in cases where an amount of transmitted data is increased, a transmission capacity of media data such as video-audio data runs short. In this case, there is a problem that a data signal to be transmitted cannot be transmitted. To avoid this problem, it has been proposed to suppress an amount of the electronic program guide data to be transmitted.
The configuration of a conventional data sending-out device disclosed in Published Unexamined Japanese Patent Application No. H8-289267 (1996) is shown in FIG. 1. First electronic program guide data (EPG1) produced in an EPG data producing unit 109 is multiplexed with program data produced in each of a plurality of multiplexers 104-2 to 104-8. In contrast, the first electronic program guide data and second electronic program guide data (EPG2) covering a wider range than that of the first electronic program guide data (EPG1) are multiplexed with promotion program data produced in a promotion channel producing unit 102. Therefore, in each normal transmission channel, electronic program guide data covering a comparatively narrow range is transmitted. In contrast, in cases where an amount of program data such as promotion program data transmitted through a promotion channel is comparatively small, a transmission allowable capacity of electronic program guide data in the promotion channel is comparatively large, and electronic program guide data covering a comparatively wide range is transmitted through the promotion channel. Accordingly, the shortage of a transmission capacity of programs due to the increase of electronic program guide data can be prevented.
However, in the conventional data sending-out device described above, electronic program guide data is divided and distributed to a plurality of channels to suppress an amount of electronic program guide data in each channel. Therefore, in cases where electronic program guide data cannot be distributed to the channels, in cases where the distribution of electronic program guide data is prohibited or in cases where the amount of electronic program guide data to be transmitted has been increased to such an extent that it exceeds a transmission allowable bit rate in each channel even though the electronic program guide data is divided and distributed to the channels, it is impossible to transmit the all amount of electronic program guide data. Therefore, there is a problem that important electronic program guide data cannot be transmitted, and there is a problem that the transmission of media data is adversely influenced.
The present invention is provided to solve the above-described problems, and the object of the present invention is to provide a data sending-out device in which important associated data such as important electronic program guide data is reliably transmitted and any adverse influence of associated data such as electronic program guide data on the transmission of media data is reliably prevented even when an amount of the associated data is increased.